Secondary Battery Electrolyte Additive for Low-Cobalt Cathode Diffusion
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Solution Overview
Problem
Secondary batteries with low-cobalt or cobalt-free positive electrode active materials face challenges in lithium ion diffusion rates and cycling performance due to reduced cobalt content, affecting their cycle life and high-temperature storage capabilities.
Innovation Solution
Incorporating a layered positive electrode material with a specific molecular formula and an electrolyte solution containing lithium difluoro(oxalato)borate, fluoroethylene carbonate, and lithium fluorosulfonylimide, which forms a low-impedance protective film to enhance lithium ion diffusion and stabilize the crystalline structure, thereby improving cycling and high-temperature performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If cobalt content in positive electrode active material is reduced or eliminated, then cost is reduced and environmental friendliness is improved, but lithium ion diffusion rate decreases and cycle life is affected
Solution Approach 1:
The patent introduces a specific electrolyte additive (lithium difluoro(oxalato)borate) as an intermediary substance that mediates between the low-cobalt positive electrode material and the electrolyte. This additive forms a protective interface layer that compensates for the reduced cobalt content by improving lithium ion transport kinetics at the electrode-electrolyte interface, thereby maintaining high diffusion rates despite lower cobalt content.
Solution Approach 2:
The patent changes the chemical composition parameters of the electrolyte by incorporating lithium difluoro(oxalato)borate at specific concentrations (0.5-5% by mass). This parameter change in the electrolyte composition compensates for the reduced cobalt content in the positive electrode, optimizing lithium ion diffusion kinetics and stabilizing the electrode structure during cycling.
2Reliability
If lithium difluoro(oxalato)borate content in electrolyte is increased, then lithium ion diffusion rate is improved, but gas evolution may increase
Solution Approach 1:
The patent optimizes the concentration parameter of lithium difluoro(oxalato)borate in the electrolyte to a specific range (0.5-5% by mass). Within this optimized parameter range, the additive effectively improves lithium ion diffusion without causing excessive gas evolution. The lower bound ensures sufficient protective effect, while the upper bound prevents harmful side reactions that would generate gas.
Solution Approach 2:
The patent references and builds upon previous research findings regarding the relationship between additive concentration and performance outcomes. By copying the optimal concentration range identified in prior studies and adapting it to the specific low-cobalt electrode system, the patent achieves improved diffusion rates while controlling gas evolution through established parameter boundaries.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution significantly enhances lithium ion diffusion rates, cycling performance, and high-temperature storage capabilities of secondary batteries, ensuring stable operation and extended cycle life without increasing gas evolution or deteriorating other performance metrics.
Implementation Method 1
the B atom in the lithium difluoro(oxalato)borate can fully bind to the O atom in the positive electrode active material, which better reduces the diffusion resistance of lithium ions in the bulk phase
Implementation Method 2
the B atom in the lithium difluoro(oxalato)borate can fully bind to the O atom in the positive electrode active material
Implementation Method 3
Secondary batteries rely on lithium ions to intercalate and deintercalate back and forth between the positive and negative electrodes for charging and discharging
Data Source
AI summary
A secondary battery may comprise an electrolyte solution and a positive electrode plate, wherein the positive electrode plate may comprise a layered material with a molecular formula of LiaNibCocM1dM2eOfAg, M1, M2, A, a, b, c, d, e, f, and g being as defined herein respectively; and the electrolyte solution may comprise lithium difluoro(oxalato)borate, based on the total mass of the electrolyte solution, the percentage mass content of the lithium difluoro(oxalato)borate being x %, with 0<x≤1.0, and the secondary battery satisfies c+x/10≥0.10.